The Bitwarden button does not appear in the menubar in Firefox in popups, so I don’t know how to fill passwords automatically when the form appears in a popup window.
The autofill hotkey should work (whatever you’ve got that set to). But if there is more than one possible login for the URL you can’t choose which to use.
It’s also a problem in Chrome.
I should have added that this is mainly an issue for me for credit card fields. Maybe just adding credit cards in the context menu would solve the issue ?